The present invention relates to video coding and, in particular, to video coding systems that apply perspective transforms to prediction data.
Capturing high quality video using mobile devices for storage or transmission can be difficult because captured content can change widely and rapidly. Generally, the capturing process involves video processing followed by video compression, both of which generally rely on simple motion models. While video stabilization techniques are often utilized on mobile devices, these techniques simply reduce irregularities in the camera trajectory, and they smooth, but do not eliminate distortion, due to camera translation in free space.
FIG. 1 schematically represents effects of camera rotation on video data. In many use cases, camera operators attempt to hold a camera still during image capture but cannot maintain the camera perfectly still. The camera may move on a frame-to-frame basis, which changes the camera's angle of orientation with respect to the subject being imaged. In other use cases, camera operators capture image information of moving subjects, which varies the camera's orientation with respect to different objects in a field of view, not only the subject being imaged but also background elements within the field of view.
Accordingly, the inventors have identified a need in the art for video coding techniques that normalize effects of changing orientation in image data as part of prediction.